The present invention relates to a package substrate, integrated circuit apparatus, substrate unit, surface acoustic wave apparatus, and circuit device, particularly to a surface acoustic wave device.
Today, mobile communication devices represented by portable phones which have been remarkably spread are being rapidly making smaller in size. Along with this, reduction in size and high performance are requested for parts used in the mobile communication devices. Here, frequency dividers are used for conducting branching and generating of signals in the mobile communication devices. Some frequency dividers are configured with a bandpass filter, band rejection filter, or a combination thereof, but other frequency dividers employ a surface acoustic wave apparatus on which two surface acoustic wave devices having mutually different bandpass center frequencies are mounted in order to achieve more reduction in size and higher performance.
Mounting substrates on which such a surface acoustic wave apparatus is mounted have been also made smaller in size and weight. Therefore, it is required that the surface acoustic wave apparatus is mounted on the mounting substrate in a high density manner. In some package substrates of the surface acoustic wave apparatuses, side vias are formed in a caved manner in the thickness direction inside surfaces. When such a surface acoustic wave apparatus is soldered on the mounting substrate, a soldering fillet applied on the side via is protruded so that the mounting area is increased, thereby the aforementioned request of the high density mounting cannot be achieved. Such a problem is not only true to the surface acoustic wave apparatuses, but also to general integrated circuit apparatuses on which integrated circuit devices are mounted on the package substrate.
Further, when the frequency divider is configured with two surface acoustic wave devices having mutually different bandpass center frequencies, in order that the mutual filter characteristics are not interfered, phase adjusting circuits are provided in the respective devices. The phase adjusting circuits are within the package with a multilayer structure made of ceramics (for example, alumina ceramics or glass ceramics) together with the surface acoustic wave devices to configure the package of the frequency divider which is the surface acoustic wave apparatus.
Here, a section view of the package of the frequency divider with the multilayer structure is shown in FIG. 17. In the illustrated package 100 of the frequency divider, a device mounting layer 101 on which two surface acoustic wave devices F1 and F2 having mutually different bandpass center frequencies are mounted is provided as the uppermost layer, a ground layer 102 in which ground electrodes are formed, a circuit forming layer 103 in which high frequency circuits such as phase adjusting circuits are formed, and the lowermost layer which is a substrate connecting layer 104 in which common ground electrodes or external connecting terminals are formed are positioned toward the lower layers from the uppermost layer, and the surface acoustic wave devices F1 and F2 are airtightly sealed by a cap 106. Interlayers are appropriately connected by via holes 108 in an electric manner.
Here, in the frequency divider, various elements such as specifications of high frequency circuits or wiring lengths are determined so as to have specific electric frequency characteristics. In order to obtain initial frequency characteristics, there is configured such that only the lowermost layer or uppermost layer is penetrated, and the portions in which wirings are not led there from, that is open stubs are not generated. For the purpose of that, the aforementioned ceramics capable of electrically connecting only the required interlayers are used as substrate materials, or the number of laminates is increased in order to avoid the open stubs so that wirings arc connected.
However, when the number of laminates is increased in order to avoid the open stubs, the package of the frequency divider is increased in size and cost thereof is also increased. Such a problem is not only true to the package of the frequency divider, but also to general surface acoustic wave apparatuses.
Further, in order to obtain larger output, reflectors are provided in resonators which are one of components of the surface acoustic wave device. In the package of the frequency divider to which such surface acoustic wave devices are used, temperature of the devices becomes high during operating so that large heat resistance is generated. As a result, there is generated a case where initial operating characteristics cannot be obtained so that stability of the operation is lost. Here, it is considered that radiating fins are provided in the package of the frequency divider, but the package is increased in size so that the request in the market cannot be achieved. Such a problem is not only true to the package of the frequency divider, but also to general surface acoustic wave apparatuses.